I am using a 4100 from another (previous) service

i agree with the last solution you need to input the correct ip, dns, and user name pass for you current service provider u can either get this from your old modem or ring your service provider also you need to make sure that your current modem is compatible with your current plan..eg if you have adsl2 you will need a adsl2 modem and so one so on. do some googleing or give your provider a call and get some info you will be sorted in no time

you need to check the settings since most providers has different IP addresses or different settings. you might need to reset the device in order for it to detect the settings of the new provider. I suggest you get info from the provider and read your device manual.